Waterproof electrostrictive inertial type microphone



Sept. 10, 19 3 D. P. WARD 3,103,559

WATERPROOF ELECTROSTRICHVE INERTIAL TYPE MICROPHONE Original Filed June24, 1960 3 Sheets-Sheet 1 INVENTOR flan A10 P W20 ATTORNEY$ Sept. 10,1963 D. P. WARD 03,5 9

WATERPROOF ELECTROSTRICTIVE INERTIAL TYPE MICROPHONE Original Filed June24, 1960 3 Sheets-Sheet 2 INVENTOR flow/1A0 A gar/w 6c fly M ATTORNEYSSept. 10, 1963 D. P. WARD WATERPROOF ELECTROSTRICTIVE INERTIAL TYPEMICROPHONE Original Filed June 24, 1960 3 Sheets-Sheet 3 INVENTOR 00%440A l lfieo BY M 13x21 M ATTO R N EYS United States Patent 3,103,559WATERPROOF ELECTROSTRICTIVE INERTIAL TWE MICROPHONE Donald P. Ward, 6Rosemary Lane, Quaker Hill, Conn. Original application June 24, 1960,Ser. No. 38,676, now

Patent No. 3,064,089, dated Nov. 13, 1962. Divided and this applicationJune 8, 1962, Ser. No. 207,840

1 Claim. (Cl. 179-122) (Granted under Title 35, U.S. Code (1952), sec.266) The invention described herein may be manufactured and used by orfor the Government of the United States of America for governmentalpurposes without the payment of any royalties thereon or therefor.

This invention relates in general to devices for converting acousticalenergy into corresponding electrical signals and more particularly to amicrophone for use in diving masks. This application is a division ofapplication Serial Number 68,676, filed June 24, 1960, now U.S. PatentNo. 3,064,089.

With advent of increased underwater activity such as submarines anddivers the problem of underwater communication has taken on various newaspects. Oneof these is the use of microphones in the mask of anunderwater swimmer. The microphones now in present use are standardmicrophones which have been adapted for such use. These microphones havebeen waterproofed and pressure compensated. Unfortunately, however,

after exposure to water these microphones lose their Watertightintegrity and age. Continuous preventive maintenance is required to keepthese units from serious loss of sensitivity and undue distortion. Sincethere are moving parts associated with these microphones and thepressure must be compensated it does not require undue water exposure tohamper their successful operation. In addition to this, thesemicrophones are of a relatively large physical size since they must beboth waterproof and pressure compensated. This increased size restrictsthe vision of the swimmer and results in a large cumbersome mask.Various solutions to the problem have been tried and suggested but theyhave all proved unsuccessful in one respect or another due in part tothe fact in all the cases the solutions have contemplated the redesignof existing microphones which were originally basically not designed forunderwater use. Addition of waterproofing and pressure equalizationseriously impairs the efficiency of these microphones. I

Applicant with his wide experience in underwater problems and theswimmers environment has approached the problem quite differently bydesigning an entirely diiferent microphone for meeting the basicrequirements of such underwater microphones.

An object of this invention is to provide a small compact, efiicientmicrophone.

Another object is to provide a waterproof microphone for underwater usewhich is insensitive to static pressure.

A further object is to provide an electrically and mechanically, simple,efficient, inexpensive microphone for use in a swimmers mask.

Still another object is to provide a small compact microphone that isinsensitive to static pressure, waterproof and corrosion risistant.

Other objects and advantages will be apparent from the followingdescription of some embodiments of the invention and the novel featuresthereof will be particularly pointed out hereinafter in connection withthe appended claim.

In the accompanying drawings:

FIG. 1 is a perspective of an underwater swimmers mask employing anembodiment of this invention;

FIG. 2'is a front elevation of an embodiment of this invention;

Patented Sept. 10, 1963 FIG. 3 is a cross-sectional plan approximatelyalong line 33 of FIG. 2;

FIG. 4 is a cross-sectional plan of another embodiment made inaccordance with this invention; and

FIG. 5 is a cross-sectional plan of still another embodiment made inaccordance with this invention.

FIG. 1 clearly illustrates the physical relationship and size of themicrophone of this invention with respect to the mask of an underwaterswimmer with which it can be used. The mask 10 which is placed over theface of the swimmer and tightly abuts his face along the edge 11 issecured in position by straps 12. The inner portion 13 of the mask formsa cavity which is directly in front of and covers the swimmers nose andmouth. This inner portion provides a watertight cavity permitting theswimmer to breath air supplied through hose 14 and to expel air throughhose 15. The hoses are connected to a canister 16 which contains a valveallowing the swimmer to both take in and expel air through opening 17 inthe mask. In order to communicate, the swimmer must be provided with atransducer as for example, a microphone 18, which will convert hisspeech into corresponding electrical signals that may then betransferred by waterproof cable 19 to any suitable transmitter means.Since in most cases the microphone is exposed to sea water at one timeor another such as when the swimmer surfaces and removes his mask themicrophone must be waterproof. In fabricating such a microphone in thepast, it has been the practice to start with a standard microphone andthen proceed to waterproof. This procedure results in a rather large,bulky unit which requires constant servicing in View of the fact thatexposed parts of the microphone are movably mouted and so subject toenvironmental conditions, such as salt water. A large microphone inaddition would obstruct the vision of the swimmer and require a muchlarger overall mask. The microphone of the invention may be, as isshown, readily mounted within the cavity of the mask withoutinterference either to the swimmer or the mask since it is compact,waterproof and requires very little or no maintenance.

In the embodiment of the invention illustrated in FIGS. 2 and 3 awatertight casing or enclosure 20 of any suitable lightweight pressureresistant and non corrosive material such as polyester molding, one of atype which is marketed by Du Pont Co. under the trademark Mylar, or anacrylic resin which is marketed under the trademark Plexiglas by theRohmand Haas Co., or a metal, contains an inertial mass 21, an electrodeelement 22 and carbon granules 23. The electrode 22 is of electricallyconducting material or has its inwardly facing surface coated with anelectrically conductive material and supported by the housingso as to berigidly affixed thereto as for example, by being bonded to a wall of thehousing. Although the housing can be of any desired shape it has beenfound quite satisfactory to have it cylindrical and closed at both endswith the electrode 22 disposed near one end 24. Theelectrode illustratedin FIG. 3 is a thin strip of metal such as copper and covers the entireinner end wall 24 of the housing although it is only necessary toprovide a surface area sufiicient to maintain a relatively lowresistance path between the electrode and inertial mass through thecarbon. The electrode may be fabricated so as to have an approximatelycentrally located lateral extension in a direction away from the wall24- or be provided with an electrically conducting hemispheric section 25 which abuts and is electrically connected to the electrode. Spacedfrom the opposite end wall 26 and from the electrode is an electricallyconducting inertial mass 21 of any heavy suitable material such ascopper or some other non conducting material provided one surface iselectrically conducting whose mass is substantially large so as to actas an inertia element. The inertial mass is supported within the casingfor movement in a direction between the end walls and relative to theend walls 24 and 26 of the housing as for example by springs 27 or anyother resilient compliant material which may be anchored to the Walls ofthe housing. The resilient compliant material or spring biases the massto some relative reference position intermediate of its path of travelso that it may move in either direction away from this referenceposition relative to the casing. Where the mass and the materialemployed to movably support the inertial mass is electricallyconducting, connection may be made directly thereto as for example wire28, which is sealed to and passes through the casing and is electricallyconnected to the spring 27 and thereby provides an external connectionto the inertial mass. Where the mass has only a conductive coating theconnection must be made to this coating. Likewise wire 29 is connectedto electrode 22. The inertial mass 21 is basically circular incrosssection where the housing is cylindrical and disposed coaxialtherewith. It may of course assume any shape in cross-section butpreferably the same as the casing. The surface of the inertial masswhich is disposed opposite and faces the electrode 22 is provided with arecess or cavity which is complementary to and in face to facerelationship with the lateral extension or hemisphere of the electrode.The plane of the inertial mass is approximately parallel to the plane ofthe electrode and the casing end walls. The free space within the casingcontains loosely packed carbon granules 23 which as to quantity andresistance are selected in accordance with standard design practice.

A diaphragm 30 is afiixed to th end wall 24 of the casing whereby theacoustic energy impinging upon the diaphragm is efiiciently transmittedto the casing in a direction transverse to the end walls and the planeof the inertial mass.- The diaphragm may be of any standard type ordesign and is covered by a mouthpiece 31 disposed in front and spacedfrom the diaphragm opposite the casing. The mouthpiece as illustratedhas a number of openings 32 extending from face to face so that anywater which enters or is present between the diaphragm and the mouthpiece may be easily expelled. Likewise the diaphragm can be providedwith drain holes either for use with or without the illustratedmouthpiece. The casing, diaphgarm and mouthpiece are assembled within asupport housing 36 which is open at the end facing the mouthpiece andwith its opposite end spaced from the rear end wall of the casing 20'.The above enumerated component parts of the microphone may beindividually supported within the housing or as has been shown themouthpiece prevented from moving out of the housing by an abutment 34which retains it. The outer peripheral edges of the diaphragm tightlyabut the inner face 35 of the mouthpiece and it is held there against bya spacer 3'6 which has an annular portion 37 in abutting relationshipwith the edge 38 of the diaphragm. The spacer is circular incross-section and has a passage 39' therethrough from face to face. Thepassage is enlarged at one end so as to allow free movement of theoperating portion of the diaphragm and thereby also form the annularportion 37 abutting the diaphragm edge. The casing 20 is supported bythe diaphragm and is disposed within the smaller portion of the passage39 and spaced from the walls of the passage.

With the microphone thusly assembled it is relatively simple to describeits operation. The hemispheric portion 25 of the electrode and thecomplementary recess of the inertial mass are employed so that themicrophone can be used in any physical position as for example upsidedown. Since'the carbon granules are not tightly packed and need notentirely till the space within the casing then, when the microphone isupside down at least a portion of the electrode, namely the hemisphere,will be in contact with the carbon. Sound or acoustical v-ibrationsimpinge upon the diaphragm and are transmitted to the casing which isfree to move and which is set in motion in a direction crosswise of itsend walls. The inertial mass M due to its large mass resists moving inthe direction of motion of the casing and tends to remain stationarysince it is supported by springs or a resilient compliant material. Thisin effect causes a relative displacement between the electrode and theinertial mass since the massican remain stationary while the casingresponds to the'movement of the diaphragm and, therefore, the carbongranules disposed between the electrode and the mass are eithercompressed or allowed to separate under the action of the casing. Thischanges the resistance between the electrode and the mass through thecarbon in accordance with the relative motion of the mass and thecasing. This change or alternating resistance is convertedinto acorresponding electrical signal by a DC; supply (battery 40) and theprimary of a transformer 41 which are connected in series with thesignal leads or wires 28 and 29 to form a complete loop circuitconsisting of the electrode 22, the carbon granules 23, the inertialmass 21, the transformer 41 primary and the battery All. Only analternating signal appears across the secondary of the't-ransformer 41since the battery or DC. component is effectively blocked and thisoutput signal may then be applied to any desired utilization circuitsuch as a transmitter or projector by suitable circuitry not shown.

Under certain conditions it is necessary to employ a microphone with amuch higher output so that the embodiment illustrated in FIG. 4 shouldbe employed. This microphone is identical in most respects with the onepreviously described except that a three terminal or electrode system issubstituted with its appropriate circuitry. Twoidentical electrodes 50and 51 are disposed in face to face spaced relation one located at andabutting each end wall of the casing with their hemispheric portionsdirectedtoward the center of the casing. The inertial mass 52 is locatedapproximately between the electrodes and has a pair of recess 53 and 54each disposed on an opposite face of the mass and aligned with thehemispheric portion of the facing electrode. The composition of thecomponent parts may be identical with those de- I scribed for theembodiments of FIGS. 2 and 3. The mass, and the electrodes are supportedin the same manner'as previously described. A wire is electricallyconnected to each of theelectrodes and the mass. Each of thewires 55, 56land 57 is sealed to and passes through the casing. The elect-rodeconnecting wires 55 and '57 are connected to the outer terminals of theprimary of transformer 58 whilethe inertial mass wire 56 is connectedthrough a battery59 to the primary center tap. Since the'current passingthrough one electrode is out of phase with the other, one section of thetransformer primary can be wound so that the resultant fields producedin both of the primary windings are additive and the secondary output isthereby increased. The movement and operation of this embodiment isidentical with the'first described embodiment.

It should be noted at this point that the-principle involved in thisinvention does not restrict its use to carbon granules and othertransducer-like.elements easily substituted. By way of example, FIG. 5illustrates still am other embodiment wherein the same electrode andinertial mass are employed except that an electrostrictive element issubstituted'for the carbon granules. The transducer element 60 may be abar of barium titanate or other suitable electrostricti've materialwhich has its opposite end faces coated with a layer of electricallyconducting material and which has to be polarized between these faces byany of a number of standard techniques. The electrically coated ends 6 1and 62 of the element abut approximately centrally respectively theelectrode 63 and theinertialnrass 64. The element can be bonded to theelectrode or supported in any suitable manner. If the bond and theelectrode are electrically conducting then the signal lead 65 can beconnected to the electrode otherwise it must contact the conductivecoating '61. A similar physical situation exists for the other endcoating 62 and the inertial mass and the signal lead 66 is shown here asconnected to the coating 62. As the ceramic 60 is alternately compressedand tensioned between the electrode and the biased inertial mass asignal voltage is developed across the coated surfaces 61 land 62 inaccordance with the vibratory displacement of the casing and diaphragm.This principle is well known in the art and the resultant signallikewise applied to a utilization circuit.

In accordance with this invention the microphone may be fabricated quiteeasily, made extremely small (button type microphone) and even employedas a hydrophone due to its watertight construction. Further this rigidlyencased stationary mass concept may be applied to dynamic, crystal andcondenser microphones.

It will be understood that various other changes in the details,materials and the arrangement of parts which have been herein describedand illustrated in order to explain the nature of this invention, may bemade by those skilled in the art within the principle and scope of theinvention as expressed in the appended claim.

I claim:

A compact, waiter-tight microphone suitable for use with an underwaterswimmers mask which comprises a support, a diaphragm carried by saidsupport and movable approximately back and forth rectilinearly inresponse to vibratory impulses impinging on said diaphragm, a closed,water-tight casing attached to and approximately centrally of saiddiaphragm for rectilinear movement therewith, an inertia element withinsaid casing having a pair of opposite electrically conducting surfacesand spaced from the walls of the casing, compliant resilient meanswithin said casing supporting said element in spaced relation to thewalls of the casing for rectilinear movement within the casing in thedirection of vibration of said diaphragm and biased into an intermediateposition in its path of vibratory movement, a pair of electricallyconducting members within the casing each individually spaced from oneof said conducting surfaces and disposed in face to face relation withopposite conducting surfaces of said element in the direction ofvibratory movement of said element, loose carbon granules in said casingbetween and abutting said conducting surfaces and said conductingmembers and providing a conducting path between them and a utilizationcircuit having said element and members as a part thereof,

whereby when said diaphragm is vibrated, the variable pressure of saidelement on said granules will vary the resistance of said circuit with afrequency corresponding to and an amplitude proportional to those of thevibrations of said diaphragm.

References Cited in the file of this patent UNITED STATES PATENTS

